1. Technical Field
The present disclosure relates to an ultraviolet light emitting device.
2. Description of the Related Art
Deep ultraviolet light having a wavelength of approximately 200 to 350 nm is utilized in various fields of sterilization, water purification, lithography, and illumination. Hitherto, mercury lamps have been widely used as deep ultraviolet light sources. Mercury lamps utilize a mercury glow discharge. From the perspective of the reduction of load on the environment, however, regulations for environmentally hazardous substances, such as mercury, are being tightened up, as in WEEE & RoHS directives in Europe. Thus, there is a demand for alternative light sources to mercury lamps. Mercury lamps are point emission sources. For lithography, which requires wide and uniform intensity light, therefore, mercury lamps require complex light source design.
An example of deep ultraviolet light sources free of mercury may be a deep ultraviolet light emitting diode (DUV-LED). Another example of deep ultraviolet light sources free of mercury may be an excimer lamp, which emits deep ultraviolet light by excitation of a discharge gas, such as krypton chloride (KrCl), by barrier discharge.
Still another deep ultraviolet light source free of mercury may be a deep ultraviolet light emitting device that includes a phosphor in combination with barrier discharge (see, for example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-505365 and Japanese Unexamined Patent Application Publication No. 2011-193929). This deep ultraviolet light emitting device emits deep ultraviolet light by irradiating the phosphor with vacuum ultraviolet light generated by excitation of a noble gas, such as xenon (Xe), by barrier discharge.
More specifically, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-505365 discloses a light-emitting device that produces surface-emitted ultraviolet light by applying an alternating voltage to electrodes on a substrate in a discharge space to cause electrical discharge. The discharge space contains a phosphor that emits ultraviolet light. Japanese Unexamined Patent Application Publication No. 2011-193929 discloses a surface-emitting device that includes long discharge tubes arranged in parallel. The long discharge tubes include a light-emitting layer that emits ultraviolet light. Deep ultraviolet light is produced by irradiating the light-emitting layer with vacuum ultraviolet light generated by electrical discharge. Such deep ultraviolet light emitting devices that include a phosphor in combination with barrier discharge advantageously have a high degree of freedom of shape due to flexible arrangement of local electrical discharge and possibly require no complex light source design.